1. Field of the Invention
The present invention relates generally to a bearing and a shaft, and more particularly to a bearing with hydrodynamic pressure generating grooves.
2. Description of Related Art
At present, hydrodynamic bearings are widely used in spindle motors in devices, such as compact disc (CD) drivers, digital video disc (DVD) drivers, hard disk drivers, laser beam printers, floppy disk drivers or in heat-dissipation fans. Spindle motors require a hydrodynamic bearing of small size, high rotational accuracy and long life.
A typical hydrodynamic bearing defines a bearing hole therein. A shaft is rotatably received in the bearing hole. A plurality of herringbone-shaped (i.e., branching off from a central axis) grooves are defined either in an inner circumferential surface of the bearing or in an external circumferential surface of the shaft. The grooves can accommodate lubricant, such as oil. During rotation of the shaft, the lubricant is driven by the rotating shaft. A lubricating film is thus formed in a clearance between the external circumferential surface of the shaft and the inner circumferential surface of the bearing. Accordingly, the shaft is supported by hydrodynamic shearing stress and dynamic pressure generated by the lubricating film when the lubricant flows through different cross-sections. Referring to FIG. 10, a hydrodynamic bearing 400 has a plurality of herringbone-shaped grooves 440 defined in an inner circumferential surface thereof. Each of the grooves 440 includes two branches 442. The supporting pressure is mainly determined by the dynamic pressure generated around a crossing point of the two branches 442. However, the dynamic pressure is steady and hard to be regulated due to uniform depth of each of the branches 442 along a direction of lubricant flow (shown as direction OY). Accordingly, the hydrodynamic bearing 400 having uniform depth cannot be used to carry differing loads.
A related method for manufacturing the hydrodynamic bearing 400 comprises following processes of: (a1) manufacturing a bearing preform with a bearing hole therein; and (a2) defining a plurality of hydrodynamic pressure generating grooves 440 in a bearing surface 450 of the bearing preform by chemical etching, electrolysis electric discharge or machining. However, the small size of the hydrodynamic bearing 400 results in difficulties in particularly in the making of the grooves 440 in the bearing surface 450 of the bearing preform. This makes manufacturing of the hydrodynamic bearing 400 both time-consuming and expensive. Therefore, the related method is not suitable for mass-production of the hydrodynamic bearing 400.
It is therefore desirable to provide an improved method for mass production of a hydrodynamic bearing which can be used to carry differing loads.